Optical printing and recording devices typically focus radiation from a source, such as a laser diode, onto a radiation sensitive recording medium. To provide a uniform amount of radiation per unit area on an uneven surface of the recording medium, it has generally been found necessary to provide an autofocus apparatus that operates continuously throughout the recording process.
U.S. Pat. No. 4,984,229 issued on Jan. 8, 1991 discloses an autofocus sensor and actuator device used to control the position of an objective lens in order to focus laser radiation onto a radiation sensitive recording medium. An independent source of radiation is used with a detector to provide a focus-error signal. The focus-error signal is used to control a current to an actuator having two moving coil linear motion solenoids suspended in a magnetic circuit.
One limit to recording speed is the ability to maintain the focus of the recording beam. In order to operate at higher recording speeds, it is desirable to have an autofocus system with a high frequency response. An improved frequency response can be obtained by either reducing the mass of the object being moved or increase the force. A limit to increasing the force is the amount of current which can be handled by magnetic coils and this is partially a function of the amount of heat which can be removed from the actuator. Another problem with moving coil solenoids is mechanical vibrations which occur at resonant frequencies, and these vibrations have a detrimental effect on focus. This is a common problem present in a moving coil configurations.
What is needed in the art is an actuator with linear motion, higher acceleration and reduced harmonic vibration. Also needed in order to achieve higher acceleration is a configuration to effectively dissipate the heat generated by the current flow through the electromagnetic coils. It is desired to create a more reliable and an easier to manufacture actuator than prior art designs.
This application incorporates by reference U.S. Provisional Application Nos. 60/087,277 entitled "Autofocus Actuator Device" filed on May 29, 1998 and 60/087,279 entitled "Autofocus Sensor Device" filed on May 29, 1998.
An efficient actuator with improved acceleration which has greater reliability and fewer moving parts which is can be manufactured easier than prior art devices is desired, and the present invention provides these features.